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SK Biopharmaceuticals CEO Lee Dong-hoon speaks at a press conference on Aug. 26 about the licensing deal for Opakalim.

Clinical trials of Opakalim, or BHV-7000, an epilepsy drug candidate that SK Biopharmaceuticals plans to license from US biotech company Biohaven, have hit a setback. The company plans to hold an online briefing on the morning of Sept. 11 to explain the impact of the measure and its response plans.

SK Biopharmaceuticals said in a regulatory filing on Sept. 10 that the US Food and Drug Administration had placed a partial clinical hold on the phase 2 and 3 US trials of Opakalim, known as RISE2 and RISE3. The move came about two weeks after the licensing agreement was announced on Aug. 26.

The action followed toxicity observed in a nonclinical study in which a specific metabolite of Opakalim was administered to rats. The FDA requested additional data to determine whether the toxicity could also occur in humans or whether it is limited to rodents.

Under the partial clinical hold, patients already enrolled in the trials may continue receiving treatment, but enrollment of new patients will be temporarily suspended until additional nonclinical studies are completed. SK Biopharmaceuticals said RISE3 will not be affected because patient enrollment and randomization have already been completed. The company also said the planned release of topline results in the second half of this year remains on schedule for now.

SK Biopharmaceuticals said it had already identified the toxicity finding during due diligence before signing the agreement. Following reviews by outside experts with experience in toxicology and FDA pharmacology and toxicology assessments, the company concluded that the finding was unlikely to be directly linked to human safety. It added that no adverse events directly associated with the toxicity finding have been identified in clinical trials involving more than 1,200 participants to date.

Opakalim has been selected as SK Biopharmaceuticals’ second product for direct commercialization in the US after cenobamate, marketed there as Xcopri. The agreement is worth up to $795 million, including an upfront payment and development and regulatory milestones related to the Kv7 platform, equivalent to about 1.1 trillion won at the time the deal was announced.

The total upfront payment is $400 million, consisting of $350 million upon deal closing and another $50 million one year later. Development and regulatory milestone payments could reach up to $395 million.

The licensing agreement between the two companies has not yet closed, meaning no financial transaction, including the upfront payment, has taken place.

Biohaven plans to conduct additional nonclinical studies requested by the FDA and submit the results and supporting data in an effort to have the partial clinical hold lifted. Whether and when the hold is removed will depend on the FDA’s review of the additional information.

                                                                                                         Kang Hye-won